The Women's Health Initiative (WHI) clinical trial, whose aim was to prospectively evaluate the risks and benefits of orally administered combination hormone replacement therapy in healthy women using estrogens and medroxyprogesterone acetate, was recently halted (Fletcher, S. W. et al. 2002. J. Amer. Med. Assoc. 288:366-368). The increased risks in coronary heart disease, breast cancer, stroke, and pulmonary embolism outweighed the increased benefits in colorectal cancer, endometrial cancer, hip fractures and death due to other causes, resulting in a small but statistically significant increased risk for the global index of hazard ratios among women taking these hormones. The authors pointed out, however, that their study only evaluated healthy women, not those with symptoms of hormone deficiency. Furthermore, other routes of delivery, e.g. transdermal systems, need to be studied, since it is possible that transdermal delivery may increase benefits and/or decrease risks to these patients. It was noted by the authors of the WHI study that hormone replacement therapy is still considered to be effective for relieving perimenopausal symptoms such as hot flashes.
Most clinical trials evaluating sex hormone replacement therapy have focused on estrogens and progestins, although testosterone replacement therapy in women who may be testosterone deficient is now beginning to be addressed using transdermal delivery systems, e.g. for disease states in which there is stress from chronic disease with loss of muscle mass and chronic fatigue, such as wasting syndrome in women with AIDS (Miller, K. Et al. 1998. J. Clin. Endocrinol. Metab. 83:2717-2725; Javanbakht, M. Et al. 2000. J. Clin. Endocrinol. Metab. 85:2395-2401). Testosterone replacement therapy using transdermal delivery has also been of benefit to men with symptoms of testosterone deficiency, for example in men with Parkinson's disease (Okun, M. S. et al. 2002. Arch. Neurol. 59:1750-1753). There is accumulating evidence that the sex hormones, in particular estrogens, progestins and now testosterone, are important for subjective feelings of well-being and quality of life, parameters that were not assessed in the Women's Health Initiative trial.
U.S. Pat. No. 5,935,949 discloses a method of alleviating the symptoms of fibromyalgia syndrome and chronic fatigue syndrome which involves oral administration of androgens, such as testosterone, to patients. The idea behind the use of testosterone therapy in the treatment of such conditions is that muscle pain and chronic fatigue, primary symptoms in women with fibromyalgia syndrome (FMS), relates, at least in part, to testosterone deficiency, since androgens are known to allow for increased musculature and improvement in fatigue. Indeed, a small decrease in serum free testosterone concentrations has been documented for premenopausal fibromyalgia patients relative to healthy volunteers, but significance was not achieved for postmenopausal women (Dessein, P. H. et al. 1999. Pain 83:313-319). A relationship between testosterone and pain sensation has been previously suggested (Blomqvist, A. 2000. Compar. Neurol. 423:549-551). Accumulating evidence supports the concept that sex hormones can elevate the pain threshold in an individual, for example, during pregnancy (Gintzler, A. R. 1980. Science 210:193-195), when testosterone concentrations, as well as estrogen and progesterone concentrations, are elevated (Bammann, B. L. et al. 1980. Am. J. Obstet. Gynecol. 137:293-298). The theory that testosterone can suppress pain is supported by the discovery of aromatase-positive cells in the spinal cord dorsal horn of higher vertebrates (quail), where initial processing of pain sensation occurs (Evard, H. Et al. 2000. J. Compar. Neurol. 423:552-564). The presence of aromatase, which converts testosterone to 17β-estradiol, is interesting because it is known that estrogen can induce the transcription of opiates in estrogen receptor-positive cells derived from the superficial layers of the spinal dorsal horn (Amandusson, A. et al. 1996. Neurosci. Lett. 196:25-28; Amandusson, A. et al. 1996. Eur. J. Neurosci. 8:2440-2445; Amandusson, A. et al. 1999. Pain 83:243-248), a location that is important for the synthesis of endogenous opiates. Administration of estrogen to ovariectomized female rats has been demonstrated to increase spinal cord enkephalin transcription (Amandusson, A. et al. 1999. Pain 83:243-248), and estrogen receptor-positive cells co-localize with preproenkephalin mRNA (Amandusson, A. et al. 1996. Eur. J. Neurosci. 8:2440-2445). These endogenous opiates act on enkenhalinergic neurons to mediate inhibition of nociceptive relay cells, both in primary afferent fibers as well as in pain-modulating fibers descending from the brainstem (Ma, W. Et al. 1997. Neuroscience 77:793-811). Thus, both testosterone and estrogen appear to be important for modulating the sensation of pain. However, the differential importance of androgens versus estrogens in pain sensation relative to gender remains poorly understood.
Testosterone may also act at the level of the brain. Testosterone concentrations were dramatically decreased in the brain and spinal cord of rats in response to pain-inducing subcutaneous injections of formalin into the paw. In these animals, the loss of testosterone in the central nervous system was demonstrated to be due to its metabolism by 5α-reductase to dihydrotestosterone (Amini, H. Et al. 2002. Pharmacol. Biochem. Behav. 74:199-204). These authors pointed out that dihydrotestosterone can be metabolized to 5α-androstane-3α,17β-diol, which is an effective modulator of GABAA receptor complexes in the brain. GABAA receptors are found throughout the brain, and actions of GABAA receptor modulators in the limbic system, specifically in the amygdala, are associated with feelings of fear. The GABAA receptor ion channel complex is one of the most important inhibitory ion channels in the brain. Thus, testosterone may be important not only for modulation of pain but also for feelings of emotional well-being via binding of its metabolites to the neurosteroid site of the GABAA receptor, although this remains to be demonstrated.
Other hormones such as growth hormone may also play a role in the pathogenesis and symptoms of fibromyalgia and chronic fatigue. For example, studies have shown that fibromyalgia patients fail to exhibit a proper growth hormone response to acute exercise, a response that is likely related to increased levels of somatostatin a powerful inhibitor of growth hormone synthesis (Crofford, L. J. et al. 2002. Arthr. Rheumat. 46:1136-1138; Paiva, E. S. et al. 2002. Arthr. Rheumat. 46:1344-1350). It is well known that testosterone increases growth hormone secretion. Growth hormone secretion is reduced in senescence beyond the reduced levels of secretion seen in adult life after puberty. This reduction is thought to relate to the decreased lean body mass to adipose mass ratio known to occur in some individuals in senescence. Thus, increased somatostatin levels may reflect decreased anabolism and decreased muscle mass due to decreased testosterone and growth hormone concentrations in fibromyalgia patients. As a result, therapy with growth hormone may improve the condition of patients with fibromyalgia.
It has now been found that transdermal hormone therapy in women can raise serum hormone concentrations to levels that approximate those normally found in premenopausal women, as well as relieve symptoms in patients with fibromyalgia.